Aloe is an intricate plant which contains many biologically active substances. (Cohen et al. in Wound Healing/Biochemical and Clinical Aspects, 1st ed. W B Saunders, Philadelphia (1992)). Over 300 species of Aloe are known, most of which are indigenous to Africa. Studies have shown that the biologically active substances are located in three separate sections of the aloe leaf--a clear gel fillet located in the center of the leaf, in the leaf rind or cortex of the leaf and in a yellow fluid contained in the pericyclic cells of the vascular bundles, located between the leaf rind and the internal gel fillet, referred to as the latex. Historically, Aloe products have been used in dermatological applications for the treatment of burns, sores and other wounds. These uses have stimulated a great deal of research on identifying compounds from Aloe that have clinical efficacy, particularly anti-inflammatory activity. (See, e.g., Grindlay and Reynolds (1986) J. of Ethnopharmacology 16:117-151; Hart et al. (1988) J. of Ethnopharmacology 23:61-71). As a result of these studies there have been numerous reports of Aloe compounds having diverse biological activities, including anti-tumor activity, anti-acid activity (Hirata and Suga (1977) Z. Naturforsch 32c:731-734), anti-diabetic activity, tyrosinase inhibiting activity (Yagi et al. (1987) Planta medica 515-517) and antioxidant activity (International Application Serial No. PCT/US95/07404, published Dec. 19, 1996, publication number WO 96/40182).
It has also been reported that Aloe products can stimulate the immune system. The ability of Aloe to stimulate the immune system has been attributed to polysaccharides present in the gel. (See, e.g. Day et al. (1922) J. Am. Pharm. Assoc. 11:462-463; Flagg (1959) American Perfumes and Aromatics 74:27-28, 61; Waller et al. (1978) Proc. Okla. Acad. Sci. 58:69-76; Shcherbukhin et al. (1979) Applied Biochemistry & Microbiology 15:892-896; Mandal et al. (1980) Carbohydrate Research 86:247-257; Mandal et al. (1980) Carbohydrate Research 87:249-256; Winters et al. (1981) Eco. Botany 35:89-95; Robson et al. (1982) J. Burn Care Rehab. 3:157-163; Ivan et al. (1983) Drug & Cosmetic Ind. 52-54, 105-106; Smothers (1983) Drug & Cosmetic Ind. 40:77-80; Mandal et al. (1983) Indian J. of Chem. 22B:890-893; Vilkas et al. (1986) Biochimie 68:1123-1127; Waller et al. (1994) Cosmetic Toiletries Manufacturing Worldwide 64-80; U.S. Pat. No. 5,308,838 of McAnalley et al.).
Aloe products are also used extensively in the cosmetic industry to protect skin against the harmful effects of ultraviolet radiation. (Grollier et al. U.S. Pat. No. 4,656,029, issued Apr. 7, 1987). Chronic exposure of the skin to ultraviolet radiation causes skin cancer in humans and laboratory animals. Exposure of the skin of laboratory animals to ultraviolet B (UVB) radiation (280-320 nm) causes suppression of the skins immune system, which impairs its ability to develop an immune response to UV-induced skin cancers, contact-sensitizing haptens and a variety of infectious microorganism. (See, Strickland (1994) J. Invest. Dermatol. 102:197-204, and references cited therein). Studies by Strickland et a. show that topical application of Aloe vera gel reduces the suppression of the immune system caused by UVB exposure. (Strickland (1994) J. Invest. Dermatol. 102:197-204).
The ability of native gel to reduce suppression of the immune system, is very low and irregular and also decreases with time. One hypothesis is that the UV-B protective factor is hydrolyzed by naturally occurring enzymes in the Aloe plant and/or by bacterial degradation. Therefore, it would seem likely that isolating polysaccharides from Aloe would help preserve this immunomodulatory activity. Previous prior art methods for the bulk isolation of polysaccharides from Aloe, however, do not effectively preserve the immunomodulatory activity. These methods, described for example in U.S. Pat. Nos. 4,957,907, 4,966,892 and 5,356,811, use lengthy (4-24 hours) alcohol precipitation and centrifugation steps. Given the failure of the prior art methods to effectively preserve the immunomodulatory activity of Aloe gel, it would be useful to have a procedure for the isolation of polysaccharides from Aloe that would allow the immunomodulatory activity to be retained and stabilized. The present invention provides such methods.